This invention relates to a tilt-up device for an outboard motor and more particularly to improved hydraulic arrangement for controlling the trim condition of a marine outboard drive and a method of mounting and configuring such a unit.
It is well known to provide a hydraulic assembly between the outboard drive portion of a marine propulsion unit and the transom of the watercraft for controlling the trim and tilt movement of the outboard drive. These types of hydraulic systems are well known both in connection with outboard motors and with the outboard drive portion of an inboard/outboard drive. Generally the hydraulic unit has a pair of chambers between which fluid moves in response to changes in trim condition. Normally a reciprocating type of device is used for this purpose and because of the connection of the piston rod to either the outboard drive or the hull of the watercraft, there is a difference in volume transfer for a given degree of movement. This different volume transfer is a result of the area displaced in one of the hydraulic chambers by the piston rod.
It is, therefore, a normal practice to employ a hydraulic reservoir for accommodating these volume changes. Normally the reservoir has a volume of gas over the hydraulic fluid in the reservoir so as to accommodate varying volumes of hydraulic fluid in the reservoir. Although these devices are effective, there is a danger that the gas in the reservoir can enter into the hydraulic system and render its operation unsatisfactory. This has been avoided either by providing a impermeable barrier between the fluid in the reservoir and the gas over the fluid or by mounting the unit in such a way that the gas will tend to self purge itself and return to the area above the liquid in the reservoir. However, this type of unit is frequently transported from place to place and the reservoir may not always be positioned so that the gas will be above the fluid in the reservoir. For example, if the hydraulic assembly is part of an outboard motor, the outboard motor may be moved from boat to boat and gas can become entrapped in the system.
It is, therefore, a principal object to this invention to provide an improved hydraulic unit for a marine outboard drive.
It is a further object to this invention to provide a hydraulic unit for a marine outboard drive wherein gas in the hydraulic system can not enter into the hydraulic unit even if the assembly is tilted to positions other than that in which the unit is designed to normally operate.
It is a further object to this invention to provide an improved reservoir arrangement for the hydraulic system of a marine outboard drive.
In conjunction with devices of the type previously mentioned, it is also common practice to provide a fluid pump that provides fluid to the hydraulic unit so that the tilt and trim condition of the marine outboard drive may be adjusted. At least a portion of such units are normally mounted on the outside of the transom of the watercraft. In fact, there are certain advantages in mounting the complete hydraulic assembly to the rear of the transom of the watercraft so as to minimize the use of piping and conduits. However, where this is done then the hydraulic unit can be exposed to damage.
It is, therefore, a still further object to this invention to provide an improved hydraulic unit for a marine outboard drive wherein all of the components of the hydraulic unit are mounted aft of the transom but are protected from damage by the basic components of the outboard drive.